This invention relates generally to green-emitting magnesium aluminate gallate phosphors activated by manganese and having improved characteristics attributable to minor incorporation of a particular type stabilizer additive. Specifically, the present invention represents an improvement to the same general phosphor compositions disclosed and claimed in U.S. Pat. No. 3,838,060 which is assigned to the assignee of the present invention.
Characteristics desirable in a phosphor intended for electric lamps such as fluorescent lamps are continued high brightness and resistance to oxidation at the high temperatures encountered in lamp manufacture. High temperatures are employed in lehring when the lamp envelope is heated to about 550.degree.-600.degree. C in air in order to decompose and drive out the binder used to apply the phosphor and also in sealing and exhaust of the lamp envelope. The phosphor should be able to withstand such heating without loss of brightness or other desirable characteristics. In the aforementioned U.S. Pat. No. 3,838,060 certain improvements were obtained in manganese-activated magnesium aluminate gallate phosphors by adding a minor proportion of stabilizer ion selected from the group consisting of an alkaline earth metal ion selected from the group of calcium, strontium and barium with phosphate ion. The molar ratios of alkaline earth metal ion to phosphate ion therein employed varied between approximately 1-1.6 and the resulting phosphor composition had the general formula: EQU Mg.sub.x Al.sub.2y Ga.sub.2(1-y) O.sub.3.sub.+x.sub.+z.sub.+w : Mn.sub.z, M.sub.w
wherein x is between about 0.1 and 1.2, wherein y is between about 0.1 and 0.7, wherein z is between about .01 and 0.1, and w is between about 1 .times. 10.sup.-.sup.5 and 3 .times. 10.sup.-.sup.1. In the preferred embodiment, a Ca HPO.sub.4 stabilizer additive at .067 molar concentration produced maximum brightness of the phosphor powder.